The present invention relates to a public telephone system comprising a center apparatus and a public telephone set (to be referred to as a telephone set hereinafter) for allowing speech communication using a card, wherein speech communication is inhibited when an invalid card which is illegally rewritten is used in the telephone set.
In a telephone set for allowing speech communication using a card such as a telephone card, to prevent speech communication using a so-called invalid card which is illegally rewritten, the following management for invalid cards has been performed. That is, it is uneconomical to store all invalid card numbers in a memory of each telephone set because the memory capacity of each telephone set becomes very large. For this reason, a memory is arranged in a center apparatus for managing all the telephone sets, and the numbers of invalid cards supposed to be illegally used in each telephone set are registered in the memory in correspondence with each telephone set and managed. A corresponding invalid card number is transmitted to each telephone set through a telephone line and stored in the memory of each telephone set.
When a card is inserted in a telephone set to make a call, the telephone set reads the card number of this inserted card to collate with the invalid card numbers registered in the memory. If the number of the inserted card coincides with one of the registered invalid card numbers, transmission is inhibited.
In the conventional invalid card management, since the center apparatus manages all the invalid card numbers of the telephone sets on the center apparatus side, the memory capacity of the center apparatus becomes very large, resulting in an economical disadvantage. Memory retrieval in registering and reading invalid card numbers in the center apparatus is undesirably time-consuming because the memory capacity is very large.
In registering invalid card numbers in each telephone set, the invalid card numbers are sequentially transmitted from the center apparatus to each telephone set. At the same time, to confirm the invalid card numbers registered in each telephone set, this telephone set is called to allow the center apparatus to receive the invalid card numbers therefrom. For this reason, in the center apparatus and the telephone set, a data transmission time in transmission of the invalid card numbers is undesirably prolonged, and the telephone set cannot be used for the speech communication as its primary purpose during the data transmission time.